1. Field of the Invention
This invention relates to an information recording unit and information recording and/or reproduction apparatus. Specifically, the present invention can suitably be applied to an improvement in a recording/reproduction apparatus using a scanning tunneling microscope.
2. Related Background Art
A scanning tunneling microscope (hereinafter referred to as STM) which is capable of directly observing the electron structure at the surface of a substance or in the vicinity of the surface has been developed [G. Binnig et al., Helvetica Physica Acta, 55,726 (1982) ]. This microscope enables high-resolution measurement of a real-space image of monocrystals and amorphous materials and enables observation using a low electric power such that the medium is not damaged by current. Also, it can be used to examine various materials because it can be operated in atmospheric air or solutions as well as in ultra-high vacuum. A wide range of application of this microscope is therefore expected.
Recently, recording/reproduction apparatuses to which an STM is applied have also been developed (Japanese Patent Laid-Open Publication Nos. 63-161552 and 63-161553).
These conventional recording reproduction apparatuses have a construction such as that shown in FIG. 1.
In the apparatus, a DC voltage high enough to cause a tunnel current is applied to a recording medium 8 by using a voltage applying circuit 5 and, in this state, the distance between a probe electrode (probe) 6 and the recording medium 8 is controlled so that the tunnel current is constant. Also, a pulse voltage is applied to the recording medium 8 having a switching memory effect with respect to electrical characteristics at a recording position to locally create a portion having a different electrical resistance in the recording portion.
For reproduction, the distance between the probe 6 and the recording layer is constantly maintained by using a current amplifier 7, a servo circuit 3 and a three-dimensional (3-D) driving mechanism 2 while applying a low voltage. An XY scan driving circuit 4 and the 3-D driving mechanism 2 are used to scan over the recording medium surface to make the probe 6 follow the surface so that a detection current is constant, thereby reproducing the recorded information from the amounts of control in the direction of the Z-axis corresponding to changes in electrical resistance created by recording operation and from the position of the probe on the surface. These operations are controlled by a microcomputer 1. The tunnel current starts flowing when the distance between the probe electrode 6 and the recording medium is reduced to 1 nm. High-precision working/production techniques are therefore required for components for finely controlling the probe electrode 6 and the recording medium 8.
For this recording/reproducing process, as described above, it is necessary to control the distance between the probe electrode and the recording medium with high accuracy. At the same time, there is a need to simplify this distance control for the purpose of improving the recording/reproducing apparatus for wide use.